The present invention relates to a method of scanning a charged particle beam and to a charged particle beam apparatus and more particularly, to method and apparatus for moving the scan position of a charged particle beam by means of a deflector.
A technique for moving the scan position of an electron beam on a specimen by the deflector (sometimes termed image shift) has been known. As the technique is compared with a technique for moving the scan position of an electron beam on a specimen by means of a specimen stage, the technique using the deflector has features that it can move the electron beam scan position highly precisely and speedily. As regards the image shift as above, US 2006/0219907A1 explains a technique of precisely measuring in advance an amount of movement of an electron beam on a specimen (an image shift amount) in response to a control parameter (control current) of an image shift deflector, that is, measuring a sensitivity to the image shift and registering it.
Nowadays, when there are many measuring points on one chip in a scanning electron microscope for measurement or inspection of, particularly, a semiconductor device, speedup of measurement, for example, is sought by making movement among the many measuring points on the basis of the image shift.
The image shift, however, is a technique of deviating an electron beam from the electron beam optical axis (meaning, in the present specification, an electron beam trajectory through which the electron beam can reach a specimen without being deflected) and therefore, raises a problem that under the influence of, for example, deflective function of lens, the scan position cannot sometimes be moved to a desired location.
In the technique of precisely measuring in advance the sensitivity to image shift and correcting the image shift amount as explained in US2006/0219907AI, there arises a problem that an instance cannot be dealt with in which a plurality of measuring points exist in the deflection region of image shift and the degree of image shift error differs point by point.